Abstract
We present a model for computing the total melt production rate from the decompression partial melting region beneath a mid-ocean ridge, and the maximum oceanic crustal thickness created at the ridge axis assuming an ideal melt migration mechanism. The calculations are based on a self-consistent numerical model for the thermal structure and steady-state mantle flow field at a mid-ocean ridge. The model includes the effect of decreasing the melt production rate within the partial melting region by melt extraction as the residual mantle matrix becomes increasingly difficult to melt. Thus the melt fraction depends not only on temperature and pressure determined by the location beneath the ridge axis (the Eulerian description) but also on the accumulated melt extraction since the upwelling mantle matrix enters the partial melting region determined by the location along the flow-line path (the Langrangian description). This effect has been neglected by previous models. The model can predict the size of the melting region and the locations of the boundaries between mantle, residual mantle, and the partial melting region for a given spreading rate, also the distribution of the melt depletion and the mean melting depth. Given the observed average thickness of oceanic crust (∼6 km), which is relatively independent of spreading rate, the model results also provide a constraint on the overall efficiency of melt migration to the ridge axis; the efficiency must decrease from 100% at 10 mm/yr to about 60% at fast spreading rates (>50 mm/yr). Although this reduction may be partially due to the increasing size of the melting region with increasing spreading rate, it still requires less efficient melt migration near the ridge axis at fast spreading rate. We found that the calculated crustal thickness is very sensitive to the mantle temperature. For a normal mantle temperature of 1350°C, the model can generate the observed 6 km oceanic crust over the global range of spreading rates, while the anomalous thicker crusts of the Iceland hotspot and the Reykjanes Ridge are related to higher mantle temperatures associated with the hotspot. Finally, by comparing our model results with previous ones we found that neglecting variations of the melting relations of the residual mantle matrix with melt removal will overestimate the crustal thickness by at least a factor of 1.7.
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References
Ahern, J. L., andTurcotte, D. L. (1979),Magma Migration Beneath an Ocean Ridge, Earth Planet. Sci. Lett.45, 115–122.
Bergman, E. A., andSolomon, S. C. (1984),Source Mechanisms of Earthquakes near Mid-ocean Ridges from Body Waveform Inversion: Implications for the Early Evolution of Oceanic Lithosphere, J. Geophys. Res.89, 11415–11441.
Bunch, A. W. H. andKennett, B. L. N. (1980),The Crustal Structure of the Reykjanes Ridge at 59°30′N, Geophys. J. Roy. Astr. Soc.61, 141–166.
Byerlee, J. D. (1978),Friction of Rocks, Pure and Appl. Geophys.116, 615–626.
Cawthorn, R. G. (1975),Degrees of Melting in Mantle Diapirs and the Origin of Ultrabasic Liquids, Earth Planet. Sci. Lett.27, 113–120.
Chen, Y. (1988),Thermal Model of Oceanic Transform Faults, J. Geophys. Res.93, 8839–8851.
Chen, Y. (1989),Dynamics of Mid-ocean Ridge Systems, Ph.D. Thesis, Princeton University, Princeton, N.J., 221 pp.
Chen, Y. (1992),Oceanic Crustal Thickness versus Spreading Rate, Geophys. Res. Lett.19, 753–756.
Chen, Y., andMorgan W. J. (1990a),Rift Valley/No Rift Valley Transition at Mid-ocean Ridges, J. Geophys. Res.95, 17,751–17,581.
Chen, Y., andMorgan, W. J. (1990b),A Nonlinear-rheology Model for Mid-ocean Ridge Axis Topography, J. Geophys. Res.95, 17,583–17,604.
Detrick, R. S., Buhl, P., Vera, E., Mutter, J., Orcutt, J., Madsen, J., andBrocher, T. (1987),Multi-channel Seismic Imaging of a Crustal Magma Chamber along the East Pacific Rise, Nature326, 35–41.
Forsyth, D. W. (1993),Crustal Thickness and the Average Depth and Degree of Melting in Fractional Melting Models of Passive Flow Beneath Mid-ocean Ridges, J. Geophys. Res.98, 16,073–16,079.
Henstock, T. J., Woods, A. W., andWhite, R. S. (1993),The Accretion of Oceanic Crust by Episodic Sill Intrusion, J. Geophys. Res.98, 4143–4154.
Klein, E. M., andLangmuir, C. H. (1987),Global Correlations of Ocean Ridge Basalt Chemistry with Axial Depth and Crustal Thickness, J. Geophys. Res.92, 8089–8115.
Klein, E. M., andLangmuir, C. H. (1989),Local Versus Global Variations in Ocean Ridge Basalt Composition: A Reply, J. Geophys. Res.94, 4241–4252.
McKenzie, D. P. (1967),Some Remarks on Heat Flow and Gravity Anomalies, J. Geophys. Res.72, 6261–6273.
McKenzie, D. P. (1984),The Generation and Compaction of Partially Molten Rock, J. Petrology25, 713–765.
McKenzie, D. P. (1985),The Extraction of Magma from the Crust and Mantle, Earth Planet. Sci. Lett.74, 81–91.
McKenzie, D. P., andBickle, M. J. (1988),The Volume and Composition of Melt Generated by Extension of the Lithosphere, J. Petrology29, 625–679.
Morgan, W. J.,Heat flow and vertical movements of the crust. InPetroleum and Global Tectonics (Fischer A. G., and Judson, S., eds.) (Princeton University Press, Princeton, N. J. 1975).
Oxburgh, E. R., andParamentier, E. M. (1977),Compositional and Density Stratification in Oceanic Lithosphere—Causes and Consequences, J. Geol. Soc. Lond.133, 343–355.
Oxburgh, E. R.,Heat flow and magma genesis. InPhysics of Magmatic Processes (Hargraves, R. B., ed.) (Princeton University Press, Princeton, N. J. 1980).
Parsons, B., andSclater, J. G. (1977),An Analysis of the Variation of Ocean Floor Bathymetry and Heat Flow with Age, J. Geophys. Res.82, 803–827.
Phipps Morgan, J. (1987),Melt Migration Beneath Mid-ocean Spreading Centers, Geophys. Res. Lett.14, 1238–1241.
Phipps Morgan, J., andChen, Y. J. (1993a),The Genesis of Oceanic Crust: Magma Injection, Hydrothermal Circulation, and Crustal Flow, J. Geophys. Res.98, 6283–6297.
Phipps Morgan, J., andChen, Y. J. (1993b),The Dependence of Ridge-axis Morphology and Geochemistry on Spreading Rate and Crustal Thickness, Nature364, 706–708.
Phipps Morgan, J., Parmentier, E. M., andLin, J. (1987),Mechanisms for the Origin of Mid-ocean Ridge Axial Topography: Implications for the Thermal and Mechanical Structure of Accreting Plate Boundaries, J. Geophys. Res.92, 12823–12836.
Phipps Morgan, J., andForsyth, D. W. (1988),Three-dimensional Flow and Temperature Perturbations due to a Transform Offset: Effects on Oceanic Crustal and Upper Mantle Structure. J. Geophys. Res.93, 2955–2966.
Reid, I. D., andJackson, H. R. (1981),Oceanic Spreading Rate and Crustal Thickness, Mar. Geophys. Res.5, 165–172.
Scott, D. R., andStevenson, D. J. (1989),A Self-consistent Model of Melting, Magma Migration and Buoyancy-driven Circulation Beneath Mid-ocean Ridges, J. Geophys. Res.94, 2973–2988.
Sleep, N. H., andWindley, B. F. (1982),Archean Plate Tectonics: Constraints and Inferences, J. Geol.90, 363–379.
Sparks, D. W., andParmentier, E. M. (1991),Melt Extraction from the Mantle Beneath Spreading Centers, Earth Planet. Sci. Lett.105, 368–377.
Spiegelman, M., andMcKenzie, D. (1987),Simple 2-D Models for Melt Extraction at Mid-ocean Ridges and Island Arcs, Earth Planet. Sci. Lett.83, 137–152.
Stolper, E., Walker, D., Hager, B. H., andHays, J. F. (1981),Melt Segregation from Molten Source Regions the Importance of Melt Density and Source Region Size, J. Geophys. Res.86, 6261–6271.
Toomey, D. R., Solomon, S. C., Purdy, G. M., andMurray, M. H. (1985),Microearthquakes Beneath the Median Valley of the Mid-Atlantic Ridge near 23°N: Hypocentres and Focal Mechanisms, J. Geophys. Res.90, 5443–5458.
White, R. S. andMcKenzie, D. P. (1989a),Magmatism at Rift Zones: The Generation of Volcanic Continental Margins and Flood Basalts, J. Geophys. Res.94, 7685–7729.
White, R. S., andMcKenzie, D. P. (1989b),Volcanism at Rifts, Scientific American, 62–71, Jul.
Wiens, D. A., andStein, S. (1984),Intraplate Seismicity and Stresses in Young Oceanic Lithosphere, J. Geophys. Res.89, 11442–11464.
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Chen, Y.J. Constraints on melt production rate beneath the mid-ocean ridges based on passive flow models. PAGEOPH 146, 589–620 (1996). https://doi.org/10.1007/BF00874735
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DOI: https://doi.org/10.1007/BF00874735